Influence of Fe(III) doping on the crystal structure and properties of hydrothermally prepared β-Ni(OH) 2 nanostructures

This paper systematically examines the influence of the level of Fe(III) doping on the crystal structure and other properties of Ni(OH)(2). Reference beta-Ni(OH)(2) and Fe-doped Ni(OH)(2) samples were synthesized by hydrothermal precipitation of mixed Ni(II) and Fe(III) nitrate aqueous solutions in a highly alkaline medium. The samples were investigated using X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (FE-SEM and TEM), energy dispersive X-ray spectroscopy (EDS), Mossbauer spectroscopy, magnetic measurements, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy, thermogravimetric analysis (TGA) and electrochemical measurements. Incorporation of Fe in beta-Ni(OH)(2) by cation substitution was confirmed from the shifts in position of XRPD lines due to the difference in the ionic radius of Fe3+ and Ni-2. The Fe-3-for-Ni2+ substitution in beta-Ni(OH)(2) caused formation of an interstratifled structure with beta-Ni(OH)(2) and alpha-Ni(OH)(2) structural units interconnected within the same structural layers and crystallites. Mossbauer spectra revealed the presence of Fe3+ ions in highly distorted octahedral sites, presumably at the boundary between the alpha-Ni(OH)(2) and beta-Ni(OH)(2) structural units within the same structural layer. Electrochemical measurements showed significant increase in oxygen evolution reaction (OER) catalytic activity of Fe-doped Ni(OH)(2) compared to pure phase. (C) 2018 Elsevier B.V. All rights reserved